How to retry idempotent operations with a mock in Python

import random
import time
from unittest.mock import Mock


def idempotent_operation(value):
    """Simulate an idempotent operation that sometimes fails."""
    if random.random() < 0.6:  # 60% failure rate
        raise ConnectionError("Temporary failure")
    return value * 2


def retry_with_backoff(operation, max_attempts=3, base_delay=0.1):
    """Retry an idempotent operation with exponential backoff."""
    for attempt in range(max_attempts):
        try:
            result = operation()
            print(f"Attempt {attempt + 1}: Success -> {result}")
            return result
        except ConnectionError as e:
            print(f"Attempt {attempt + 1}: Failed ({e})")
            if attempt < max_attempts - 1:
                time.sleep(base_delay * (2 ** attempt))
    print("All attempts failed")
    return None


if __name__ == "__main__":
    # Mock the operation to control failure/success deterministically
    operation_mock = Mock(side_effect=[ConnectionError("Down"), ConnectionError("Down"), 42])

    # Patch random to make the real function predictable for comparison
    original_random = random.random
    random.random = lambda: 1.0  # Force failure in real function

    print("--- Using mocked operation (deterministic) ---")
    result = retry_with_backoff(operation_mock)
    print(f"Final result: {result}")

    print("\n--- Using real operation patched to always fail ---")
    result2 = retry_with_backoff(lambda: idempotent_operation(21))
    print(f"Final result: {result2}")

    # Restore original random
    random.random = original_random